Abstract: In Sweden, children typically start compulsory school the year they turn 7. Individuals born around the new year have about the same date of birth but enter school at different ages. We exploit this source of exogenous variation to identify effects of age at school entry on educational attainment and long-run labor market outcomes. Using data for the entire native population born 1935-55, we find that school entry age raises educational attainment. We show that the comprehensive school reform (which postponed tracking until age 16) reduced the effect of school starting age on educational attainment. We also trace the effects of school starting age on prime-age earnings, employment, and wages. On average, school starting age only affects the allocation of labor supply over the lifecycle; prime-age earnings is unaffected, and there is a negative effect on discounted life-time earnings. But for individuals with low-educated parents, and to some extent women, we find that prime-age earnings increase in response to age at school start.